129,468 research outputs found
A Test of Photometric Redshifts for X-ray Selected Sources
We test the effectiveness of photometric redshifts based upon galaxy spectral
template fitting for X-ray luminous objects, using a sample of 65 sources
detected by Chandra in the field of the Caltech Faint Galaxy Redshift Survey
(CFGRS). We find that sources with quasar-dominated spectra (for which galaxy
spectral templates are not appropriate) are easily identified, and that
photometric redshifts are robust for the rest of the sources in our sample.
Specifically, for the 59 sources that are not quasar-dominated at optical
wavelengths, we find that the photometric redshift estimates have scatter
comparable to the field galaxy population in this region. There is no evidence
for a trend of increasing dispersion with X-ray luminosity over the range L_X =
10^39 - 5x10^43 erg/s, nor is there a trend with the ratio of X-ray to optical
flux, f_X/f_R. The practical implication of this work is that photometric
redshifts should be robust for the majority (~90%) of the X-ray sources down to
f_X ~ 10^-16 erg/s/cm^2 that have optical counterparts brighter than R ~ 24.
Furthermore, the same photometry can be easily used to identify the sources for
which the photometric redshifts are likely to fail. Photometric redshift
estimation can thus be utilized as an efficient tool in analyzing the
statistical properties of upcoming large Chandra and XMM-Newton data sets and
identifying interesting subsamples for further study.Comment: To appear in ApJ (6 pages, 6 figures). Replaced with accepted versio
Satellite and surface geophysical expression of anomalous crustal structure in Kentucky and Tennessee
An equivalent layer magnetization model is discussed. Inversion of long wavelength satellite magnetic anomaly data indicates a very magnetic source region centered in south central Kentucky. Refraction profiles suggest that the source of the gravity anomaly is a large mass of rock occupying much of the crustal thickness. The outline of the source delineated by gravity contours is also discernible in aeromagnetic anomaly patterns. The mafic plutonic complex, and several lines of evidence are consistent with a rift association. The body is, however, clearly related to the inferred position of the Grenville Front. It is bounded on the north by the fault zones of the 38th Parallel Lineament. It is suggested that such magnetization levels are achieved with magnetic mineralogies produced by normal oxidation and metamorphic processes and enhanced by viscous build-up, especially in mafic rocks of alkaline character
The Moho as a magnetic boundary
Magnetic data are presented for mantle derived rocks: peridtites from St. Pauls rocks, dunite xenoliths from the kaupulehu flow in Hawaii, as well as peridolite, dunite and eclogite xenoliths from Roberts Victor, Dutoitspan, Kilbourne Hole, and San Carlos diatremes. The rocks are paramagnetic or very weakly ferromagnetic at room temperature. Saturation magnetization values range from 0.013 emu/gm to less than 0.001 emu/gm. A review of pertinent literature dealing with analysis of the minerals in mantle xenoliths provides evidence that metals and primary Fe3O4 are absent, and that complex CR, Mg, Al, and Fe spinels dominate the oxide mineralogy. All of the available evidence supports the magnetic results, indicating that the seismic MOHO is a magnetic boundary
Groups of Fibonacci type revisited
This article concerns a class of groups of Fibonacci type introduced by Johnson and Mawdesley that includes Conway?s Fibonacci groups, the Sieradski groups, and the Gilbert-Howie groups. This class of groups provides an interesting focus for developing the theory of cyclically presented groups and, following questions by Bardakov and Vesnin and by Cavicchioli, Hegenbarth, and Repov?s, they have enjoyed renewed interest in recent years. We survey results concerning their algebraic properties, such as isomorphisms within the class, the classification of the finite groups, small cancellation properties, abelianizations, asphericity, connections with Labelled Oriented Graph groups, and the semigroups of Fibonacci type. Further, we present a new method of proving the classification of the finite groups that deals with all but three groups
Dynamics of Co-translational Membrane Protein Integration and Translocation via the Sec Translocon
An important aspect of cellular function is the correct targeting and delivery of newly synthesized proteins. Central to this task is the machinery of the Sec translocon, a transmembrane channel that is involved in both the translocation of nascent proteins across cell membranes and the integration of proteins into the membrane. Considerable experimental and computational effort has focused on the Sec translocon and its role in nascent protein biosynthesis, including the correct folding and expression of integral membrane proteins. However, the use of molecular simulation methods to explore Sec-facilitated protein biosynthesis is hindered by the large system sizes and long (i.e., minute) timescales involved. In this work, we describe the development and application of a coarse-grained simulation approach that addresses these challenges and allows for direct comparison with both in vivo and in vitro experiments. The method reproduces a wide range of experimental observations, providing new insights into the underlying molecular mechanisms, predictions for new experiments, and a strategy for the rational enhancement of membrane protein expression levels
Atom lithography using MRI-type feature placement
We demonstrate the use of frequency-encoded light masks in neutral atom
lithography. We demonstrate that multiple features can be patterned across a
monotonic potential gradient. Features as narrow as 0.9 microns are fabricated
on silicon substrates with a metastable argon beam. Internal state manipulation
with such a mask enables continuously adjustable feature positions and feature
densities not limited by the optical wavelength, unlike previous light masks.Comment: 4 pages, 4 figure
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